Cetane-Improving Component for Diesel Fuels and Diesel Fuels Containing it

ABSTRACT

Cetane improver for diesel fuels, characterized in that it comprises at least one ester of stearic acid, selected from the esters of linear or branched monoalcohols containing 1 to 6 carbon atoms: a) added in the pure state to a mixture of at least one vegetable or animal oil ester in crude or partially hydrogenated form b) or else included in a mixture of esters of one or more vegetable and/or animal oils, in crude or partially hydrogenated form, the mixtures of saturated or unsaturated esters being such that the ratio by mass of the amount of stearic ester(s) to the total sum of the amounts of unsaturated esters present in the vegetable or animal oil esters varies from 1% to 12%, and the unsaturated fatty acid esters being esters of mono or polyunsaturated acids containing at least 18 carbon atoms with monoalcohols.

FIELD OF THE INVENTION

The present invention relates to a component which improves cetanewithout degrading the performance under cold conditions and theoxidation stability of diesel fuels, as well as to diesel fuelscontaining this component. It relates more particularly to theincorporation into diesel fuels of components deriving from products ofvegetable or animal origin.

TECHNOLOGICAL BACKGROUND

Fuels containing vegetable oil derivatives have a reduced emission leveland an increased biodegradability, but they habitually demonstrate avery high oxidation sensitivity and show very poor properties under coldconditions. Despite these drawbacks, sales of fuels containing thesederivatives have increased significantly in recent years as theproduction of these derivatives becomes more competitive withconventional fuels derived from crude oil. In particular, the productionof such fuels permits a more positive view of the future as oil reservesdiminish. However, the poor properties of these components under coldconditions and their high oxidation sensitivity have for a long timeconstituted factors limiting their use in high concentrations in dieselfuels, as there is a risk that their physical and chemicalcharacteristics will jeopardize the satisfactory operation of commercialengines. Taking account of these engines, it is at present difficult touse these derivatives at levels exceeding 5% in diesel fuels and obtainoptimum efficiency.

These vegetable oil derivatives are often products of thetransesterification of vegetable or animal oil triglycerides. They havea high cetane number corresponding to a good performance of the fuelupon combustion. For these derivatives, a cetane number of at least 47is required according to United States standards (ASTM D 6751) and 51 incertain European countries (such as Germany for example). Since cetanenumbers correlate with low nitrogen oxide emissions, the addition ofthese products can be very significant for the production of dieselfuels to which products obtained from vegetable and animal oils havebeen added.

G. Knothe et al., Fuel 82, 971-975 (2003) gives the cetane numbers ofesters of many fatty acids such as palmitic acid, stearic acid, oleic orlinoleic acid and in particular the beneficial effect of increasing thelength and the saturated character of the chain on the cetane number, asis the case for esters of palmitic acid and stearic acid. It is observedmoreover, that the linear or branched character of the ester has noeffect.

In European application EP 1484385, a biofuel is described containing100% by weight of a mixture of esters of palm oil, this mixture having alow pour point, particularly suitable for cold countries withoutaddition of additives. This biofuel is produced by esterification of amixture of C18 (stearic), C18:1 (oleic) and C18:2 (linoleic) fatty acidsby methanol or ethanol, followed by the fractional distillation of themethyl and ethyl esters, finally crystallization. The biofuel isprepared by mixing these fractions originating from the distillation ofpalm oil. It is used as a fuel, on environmental principles, as asubstitute for diesel fuels, obtained from palm oil and standardmixtures of palm oil esters.

Olefinic fatty acid esters contain more than 16 carbon atoms and inparticular methyl esters are known for their good properties under coldconditions but also for their high oxidation sensitivity. Moreover,although they have the advantage of high cetane numbers, saturated fattyacid esters with up to 18 carbon atoms are known for their tendency todeteriorate the flow properties of biodiesels.

SUMMARY OF THE INVENTION

It was found that among these esters of saturated fatty acids theaddition of at least one saturated acid ester with a carbon chain havingat least 16 carbon atoms, in particular at least one stearic acid ester,hereafter called a stearic ester, in a particular concentration in adiesel fuel, was able not only to improve the cetane number of this fuelbut to stabilize its oxidation resistance, without significantlydeteriorating its performance under cold conditions.

The present invention relates to a cetane-improving andoxidation-stabilizing component for diesel fuels, comprising at leastone stearic ester chosen from esters of linear or branched monoalcoholscontaining 1 to 6 carbon atoms

a) in pure state, added to a mixture of at least one vegetable or animaloil ester in crude or partially hydrogenated form

b) or included in a mixture of esters of one or more vegetable and/oranimal oils in crude or partially hydrogenated form,

the mixtures of saturated and unsaturated esters being such that theratio by mass of the level of stearic ester(s) to the sum of the levelsof unsaturated esters present in the esters of vegetable or animal oilsvaries from 1 to 12% by weight, and the esters of unsaturated fattyacids being esters of unsaturated mono- or polyacids containing at least18 carbon atoms, and of monoalcohols.

DETAILED DESCRIPTION OF EMBODIMENTS

In the remainder of the present description, the reference to vegetableor animal oil stearic esters will cover the esters resulting from theesterification of vegetable and animal oils, whether totally orpartially hydrogenated, extracted or not. The framework of the presentinvention will not be exceeded if the stearic acid ester were used inpure state, optionally in a mixture with at least one ester of anunsaturated linear acid having more than 16 carbon atoms.

The component is used in a concentration such that the stearic esterscontribute to the improvement of the cetane number without deterioratingthe performance of the fuel under cold conditions and while improvingthe oxidation stability of the hydrocarbons.

The ratio by mass of the esters [stearic ester(s)/esters of unsaturatedfatty acid(s) having 18 carbon atoms and more] generally varies from 1to 12%, and, preferably, is comprised between 5 and 9.6% and morepreferably between 7 and 9.0%.

The stearic ester is advantageously chosen from the esters of linear orbranched monoalcohols containing 1 to 6 carbon atoms. In particularmethyl or ethyl esters, or also n-propanol, isopropanol, n-butanol ortert-butanol esters, and more particularly methyl or ethyl esters ofstearic acid are preferred.

The stearic ester can be of natural or synthetic origin. Stearic estersare present in all esters of vegetable or animal oils. In particular, itmay have come from partial or total hydrogenation of esters of vegetableor animal oils with a high level of unsaturated esters of C18 fattyacids, preferably linear, such as the esters of oleic, linoleic andlinolenic acids. The stearic ester can be introduced into a fuel as partof an ester of a vegetable or animal oil or as a part resulting from themixing of several esters of vegetable and/or animal oils. The scope ofthe invention will not be exceeded if, instead of using the productsresulting from crude esterification, each ester contained were refinedand/or separated by type of esterified acid and these esters of acidswere mixed in the proportions required for the implementation of theinvention in fuel.

Among the other esters present in the mixtures, the unsaturated estersof acids containing 18 carbon atoms and more, and in particular theesters of mono- or polyunsaturated acids containing 18, 20 or 22 carbonatoms, are preferred mixed with the stearic esters, due to theirbeneficial effect on the properties of diesel fuels under coldconditions: they are effective for moderating the negative effect of thestearic esters on these properties. The preferred unsaturated esters arethe esters of oleic, linoleic or linolenic acids. The esters ofunsaturated fatty acids can be of natural or synthetic origin. They arepresent in the esters of vegetable or animal oils in concentrations thatcan vary according to the type of esterified oil. The stearic acid esterpresent in these mixtures makes it possible to limit the well knownoxidation of these unsaturated esters and to stabilize this effect. Theincrease in the cetane number and the improved operability of the fuelsunder cold conditions are optimum when there is an appropriatecombination of stearic ester with esters of unsaturated acids containingat least 18 carbon atoms, preferably linear.

It is well known that vegetable or animal oils contain triglycerides ofmonocarboxylic fatty acids. The number and nature of the acid residuesin the composition of the glycerides define the type of each of theseoils. The mixtures of esters can optionally come from a mixture ofesters of vegetable or animal oils such as in particular esters of colzaoils (methyl or ethyl ester of colza for example), palm oil esters(methyl or ethyl palm ester for example), pine oil esters (methyl orethyl pine ester for example), soya oil esters (methyl or ethyl soyaester for example), sunflower oil esters (methyl or ethyl sunflowerester for example), maize oil esters (methyl or ethyl maize ester forexample), safflower oil esters (methyl or ethyl safflower ester forexample), cotton oil esters (methyl or ethyl cotton ester for example),coriander oil esters (methyl or ethyl coriander ester for example),mustard oil esters (methyl or ethyl mustard ester for example), tallowoil ester (methyl or ethyl tallow ester for example) and all otheresters containing stearic esters and/or esters of acids containing atleast 18 unsaturated carbon atoms.

The esterification of triglycerides of fatty acids present in these oilscan be carried out according to the known methods. In particular it canbe carried out by alcoholysis, by means of the alcohols mentionedpreviously, as described by J.-C. Guibet et al., Carburants et moteurs,Ed. Technip Paris, or according to European patent application EP 860494.

Within the framework of the present invention, it is possible to useesters of several vegetable and/or animal oils in a mixture to introducethe necessary quantities of stearic esters and esters of unsaturatedfatty acids having at least 18 carbon atoms. The mixture canadvantageously comprise two, three or more esters of different oils. Itis well understood that suitable mixtures are limited to those whichmake it possible to arrive at a value of the ratio by mass [stearicester(s)/sum of the esters of C18 and above unsaturated acids] comprisedbetween 1 and 12%, preferably varying from 5 to 9.6% and even moreadvantageously from 7 to 9%.

The present invention also relates to the use of a cetane-improving andoxygen-stabilizing component for diesel fuels, as defined previously,for the preparation of a diesel fuel with an improved cetane numberwithout deteriorating the low-temperature and oxidation stabilityproperties of said fuel, starting from a mixture of esters of vegetableand/or animal oils.

Another subject of the present invention also relates to a diesel fuelcomprising:

-   -   at least one hydrocarbon from distillates with a boiling point        varying from 180 to 350° C.,    -   at least one component comprising at least one saturated ester        having more than 16 carbon atoms, preferably comprising at least        one stearic ester chosen from the esters of linear or branched        monoalcohols containing 1 to 6 carbon atoms:        -   a) in pure state, mixed with at least one ester of an            unsaturated linear fatty acid having at least 18 carbon            atoms,        -   b) in pure state, added to a mixture of at least one ester            of a vegetable or animal oil in crude or partially            hydrogenated form        -   c) or included in a mixture of one or more esters of            vegetable and/or animal oils in crude or partially            hydrogenated form,    -   the mixtures of saturated and unsaturated esters being such that        the ratio by mass of the level of stearic ester(s) to the sum of        the levels of unsaturated esters present in the esters of animal        or vegetable oils varies from 1 to 12%, the esters of        unsaturated fatty acids being esters of unsaturated mono- or        polyacids containing at least 18 carbon atoms, and esters of        monoalcohols, and    -   the stearic acid ester level in said fuel being at least 0.5% by        mass.

The hydrocarbons have come from oil distillation cuts, but also frombiomass, essentially paraffinic hydrocarbon mixtures resulting from theconversion of gas into hydrocarbons or from any other process allowingall or some of such mixtures or a mixture of these various sources ofhydrocarbons to be obtained.

The esters of saturated or unsaturated fatty acids necessary for therealization of the invention were defined earlier in the presentdescription.

If the stearic ester is introduced into the fuel in pure state or in anyother form whatever, its concentration will have to be kept below orequal to 2.4% by mass.

When the stearic ester is introduced into the fuel, mixed with othercompounds such as for example the esters of vegetable or animal oils,ester mixtures of one or more vegetable and/or animal oils, the stearicester level of the fuel can vary between 0.5 and 2.4%, preferablybetween 0.5 and 1.2% and the ratio by mass stearic ester/sum of theesters of unsaturated acids present in the fuel can vary between 1 and12%, preferably between 5 and 9.6% by mass and more particularly between7 and 9% by mass.

Mixtures of esters of several vegetable and/or animal oils areadvantageously used to achieve the optimum composition of stearicesters/unsaturated esters comprising at least 18 carbon atoms. It iswell understood that the optimum mixtures are limited to those whichmake it possible to achieve, according to the quantity of stearic esterpresent, a final level of stearic ester which is always below or equalto 2.4% weight, a value of the ratio by mass [stearic ester/sum of theester(s) of unsaturated acids] comprised between 1 and 12% andpreferably comprised between 5 and 9.6% and more particularly between 7and 9%.

Preferably, whatever the composition of the component, the stearic esterlevel will advantageously be comprised between 0.5 and 1.2% by weight inthe fuel and the ratio by mass [stearic ester/sum of the ester(s) ofunsaturated acids] is comprised between 7 and 9%.

When the stearic esters are in the presence of strong concentrations ofat least one second C16 saturated acid ester, the palmitic ester, thismust be taken into account. In fact, the effects of these esters areclose to those of stearic esters, in particular regarding theperformance of the fuel under cold conditions. The Applicant thusobserved that the sum of the stearic esters and the palmitic esters,i.e. the sum of the esters of saturated C16 and C18 acids, was a factorlimiting the mixtures of esters of vegetable oil in diesel fuels. Thus,the quantity of saturated C16 and C18 esters cannot exceed 10% by weightof the fuel. By exploiting the combination of esters of vegetable and/oranimal oils while still respecting the conditions described above, thequantity of esters of vegetable oils contained in the fuels can thus beincreased very substantially, up to over 10% by mass, without beinglimited to colza oil esters only. Thus it is possible in a preferredfashion, to introduce esters of palm, soya and sunflower oils into thefuels at higher concentrations.

In particular, the concentration of the compound in the fuel can befixed above 10% and even 20%, to increase the cetane number while stillmaintaining the oxidation stability of the fuels with good flowproperties and filterability under cold conditions. In particular itmakes it possible for filterability additives, in particular EVAs(polyethylenevinylacetates) to have a beneficial effect on thefilterability temperature of the resulting fuel.

In order to give the fuel all the properties necessary for thesatisfactory operation of vehicle engines, said fuel can of course alsocontain other additives intended to improve the properties under coldconditions, the flow or filterability, but also anti-foaming, lubricity,conductivity, anticorrosion, detergent and de-emulsification additivesthat no person skilled in the art would forget to include, as well asbactericides.

The fuel can have a low sulphur level, preferably less than 500 ppmsulphur, advantageously less than 100 ppm.

The following examples are given to illustrate the present invention butin no way limit it.

EXAMPLES Example 1

The present example serves to demonstrate the feasibility of theintroduction of mixtures of two esters of vegetable oils of differenttypes chosen from the methyl esters of colza (EMC), soya (EMS) and palm(EMP) and the influence of these mixtures introduced in differentconcentrations into a diesel of type EN590 (GOl) and a heating oil(FODl) the characteristics of which are given in Table I below.

TABLE I GO FOD FLT (° C.) −4 −5 Cloud point (° C.) −12 −18 Transitionpoint (° C.) −4 −6 IP 387 1.01 MV15 0.8327 0.8388 Sulphur content ppm39.8 1740 Viscosity at 40° C. mm/s 2.725 2.451 Calculated cetane 50.148.5 Monoaromatics % 22.7 21.2 Diaromatics % 6.2 6.9 Polyaromatics % 0.60.6 D86 distillation Initial boiling point 167.6 168  5% 190.1 188.5 10%203 196.3 20% 224.7 210.8 30% 244.9 227 40% 260.7 242.3 50% 274.5 258.960% 288.1 274.3 70% 301.7 290.7 80% 317.1 310.1 90% 337.4 333.7 Finalboiling point 356 356.3

Table II summarizes the respective quantities in the envisaged differentesters of saturated C16 and C18 acid esters and unsaturated fatty acidshaving at least 18 carbon atoms.

TABLE II C16 C18 C18:1 C18:2 C18:3 C20 C20:1 C22 Sat Unsat Sat/Unsat MP44 6 38 10 0.5 0.5 0 0 51.5 48.5 1.061856 MC 5 2 59 21 9 0.4 1 0.5 7.991 0.086813 MT 6 5 19 68 0.5 0.5 0.5 0.5 12 88 0.136364 MSoya 10 4 23 538 0.5 0.5 0.5 15 84.5 0.177515

The mixtures according to the invention were produced by varying therespective concentrations of colza methyl ester and palm methyl esterand by varying the concentration of the mixture in each of the twohydrocarbons. Each test will be labelled Xi for the GO and Yi for theFOD as described in Table III below.

TABLE III sat C18 sat C16 + 18 sat C18/unsat C18 FLT Additive contentHydrocarbon EMP EMC % weight % weight % mass Without 200 ppm 400 ppmDiesel 100 0 0 0 0 0 −4 −14 90 0 10 0.2 0.79 2.25 −4 −13 90 10 0 0.65.15 12.37 −2 −10 90 3 7 0.3 2.1 5.28 −4 −14 90 7 3 0.5 3.84 9.33 −3 −1480 0 20 0.4 1.58 2.25 −3 −13 80 10 10 0.8 5.94 7.31 −3 −11 80 16 4 0.9898.56 10.4 −2 −9 80 20 0 1.2 10.3 12.37 −3 −8 70 0 30 0.6 2.37 2.25 −3−13 70 21 9 1.4 11.5 9.33 −2 −7 −8 70 24 6 1.6 12.8 10.35 −3 −7 −3 70 300 1.8 15.5 12.37 −3 −5 −2 FOD 100 0 0 0 0 0 −5 −16 90 0 10 0.2 0.79 2.25−5 −16 90 10 0 0.6 5.15 12.37 −4 −15 90 3 7 0.3 2.1 5.28 −6 −17 90 7 30.5 3.84 9.33 −5 −16 80 0 20 0.4 1.58 2.25 −4 −17 80 10 10 0.8 5.94 7.31−5 −15 80 16 4 0.989 8.56 10.4 −5 −13 80 20 0 1.2 10.3 12.37 −5 −11 70 030 0.6 2.37 2.25 −4 −16 70 21 9 1.4 11.5 9.33 −5 −10 −9 70 24 6 1.6 12.810.35 −5 −11 −9 70 30 0 1.8 15.5 12.37 −6 −8 −8

In this table the levels of saturated C18 and saturated C16+C18 aregiven in the middle distillate/methyl ester of fatty acid mixture.

The ratio of saturated C18/unsaturated C18 to the ratio of these estersin the mixture of fatty acid methyl esters.

Table III shows that it is possible to introduce more than 20% of amixture of esters of vegetable oils into hydrocarbons of the diesel andheating oil type, providing that the stearic ester (sat C18)concentration is always below 1.2% by weight for a minimum deteriorationof the filterability limit temperature (FLT) measured by application ofthe standard EN116 by increasing the temperature by 6° C. The FLTreactivity is not degraded and the increase remains at a level above 6°C. with respect to the mixture without additive. According to the case,it is possible to correct this deterioration by addition of a FLTadditive based on EVA (polyethylenevinylacetate). However, the additionof EVA is effective only when the ratio by mass of [saturated C18s/sumof the unsaturated C18s] is kept below or equal to 9% mass, andparticularly a level of (sat C16+C18) corresponding to the sum of thestearic and palmitic esters, always below 10% by weight in said fuel.

Example 2

In this example, apart from the cetane number and filterabilitycharacteristics of the mixtures in an EN590 type diesel, the oxidationstability characteristics of the mixtures are measured by the iodinenumber (IN) determined by standard EN14214. The description of thesecompositions is as follows (% by mass):

A=5SE+95EMC

B=40EMC+60EMP

C=30EMC+70EMP

D=70EMC+30EMP

E=8SE+92(EMC+EMS+EMP)

F=100EMC

These components A, B, C, D, E and F were added to the diesel in aproportion 20% component to 80% diesel by weight. The physico-chemicalcharacteristics of these compositions are summarized in Table IV below.

TABLE IV FLT SE/GO SE/EAG Composition IN* +EVA Cetane (% weight) (%mass) Diesel −16 −21  51 — — A 110 −13 −19^(b) 52 1.34 7.6 B 82 −9−13^(a) 54.5 1.16 7.95 C 76 −9 −13^(b) 55 1.33 9.34 D 99 −9 −19^(a) 530.76 4.6 E 107 0  −2^(b) 53.8 1.94 9.7 F 116 −13 −20^(a) 51.6 0.36 1.94*Iodine number of the diesel containing esters ^(a)addition of 100 ppmEVA ^(b)addition of 400 ppm EVA

Examples A to D according to the invention satisfy the criteria of theratio of stearic ester/unsaturated esters and oxidation stability, whilestill leading to compositions having good properties under coldconditions and an iodine number below 110.

1. Cetane-improving component for diesel fuels characterized in that itcomprises at least one stearic acid ester chosen from esters of linearor branched monoalcohols containing 1 to 6 carbon atoms: a) in purestate added to a mixture of at least one vegetable or animal oil esterin crude or partially hydrogenated form b) or included in a mixture ofesters of one or more vegetable and/or animal oils in crude or partiallyhydrogenated form, the mixtures of saturated and unsaturated estersbeing such that the ratio by mass of the level of stearic ester(s) tothe sum of the levels of unsaturated esters present in the esters ofanimal or vegetable oils varies from 1 to 12%, and the esters ofunsaturated fatty acids being esters of unsaturated mono- or polyacidscontaining at least 18 carbon atoms, and esters of monoalcohols. 2.Component according to claim 1, characterized in that the stearic acidester is chosen from methyl or ethyl esters, or from n-propanol,isopropanol, n-butanol or tert-butanol esters.
 3. Component according toclaim 1, characterized in that, in the component containing esters ofunsaturated fatty acids, the ratio by mass [stearic ester levels/sum ofthe levels of the ester(s) of unsaturated fatty acids] varies from 5 to9.6% and preferably from 7 to 9.0%.
 4. Component according to claim 1,characterized in that the esters of unsaturated fatty acids present inthe composition are esters of mono- or polyunsaturated acids, containing18, 20 or 22 carbon atoms.
 5. Component according to claim 1,characterized in that the esters of unsaturated fatty acids form part ofthe group constituted by esters of oleic, linoleic or linolenic acids.6. Component according to claim 1, characterized in that the stearicacid ester or the esters of unsaturated fatty acids are of natural orsynthetic origin.
 7. Component according to claim 1, characterized inthat the stearic acid ester or the esters of unsaturated fatty acidshave come from the transesterification of the triglycerides contained inthe vegetable and/or animal oils
 8. Component according to claim 1,characterized in that it is constituted by a mixture of esters ofvegetable oils chosen from methyl or ethyl esters of colza, palm, pine,soya, sunflower, tallow, maize, safflower, cotton, coriander, mustardand any other esters containing stearic esters and/or unsaturated estershaving at least 18 carbon atoms.
 9. Diesel fuel characterized in that itcomprises: at least one hydrocarbon from distillates with a boilingpoint varying from 180 to 350° C., at least one component comprising atleast one saturated ester having more than 16 carbon atoms, preferablycomprising at least one stearic ester chosen from the esters of linearor branched monoalcohols containing 1 to 6 carbon atoms: a) in purestate, in a mixture with at least one ester of an unsaturated linearfatty acid having at least 18 carbon atoms, b) in pure state, added to amixture of at least one ester of a vegetable or animal oil in crude orpartially hydrogenated form, c) or included in a mixture of one or moreesters of vegetable and/or animal oils in crude or partiallyhydrogenated form, the mixtures of saturated and unsaturated estersbeing such that the ratio by mass of the level of stearic ester(s) tothe sum of the levels of unsaturated esters present in the esters ofanimal or vegetable oils varies from 1 to 12%, and the unsaturated fattyacid esters being esters of unsaturated mono- or polyacids containing atleast 18 carbon atoms, and esters of monoalcohols, and the stearic acidester level in said fuel being at least 0.5% by mass.
 10. Fuel accordingto claim 9, characterized in that the stearic ester level is comprisedbetween 0.5 and 2.4%, and the ratio by mass stearic ester/sum of theesters of unsaturated acids present varies from 5 to 9.6% by weight andpreferably from 7 to 9% by weight.
 11. Fuel according to claim 9,characterized in that the stearic ester level varies from 0.5 to 1.2%.12. Fuel according to claim 9, characterized in that it comprises atleast 10% by weight of the sum of the C16 and C18 saturated esters. 13.Fuel according to claim 9, characterized in that it contains more than10% by weight of a mixture of esters of vegetable and animal oils takenin combination, preferably more than 20% by weight of such a mixture.14. Fuel according to claim 9, characterized in that the fuel containsat least one cold filterability additive.
 15. Fuel according to claim 9,which has a low sulphur level, preferably less than 500 ppm sulphur,advantageously less than 100 ppm.
 16. Use of a component according toclaim 1, for the preparation of a diesel fuel with an improved cetanenumber without deterioration of the low-temperature and oxidationstability properties of said fuel, starting from a mixture of esters ofvegetable and/or animal oils.